The invention relates to the process of non-destructively sorting small items by assessment of the condition of softness, particularly for small fruits or vegetables. Small food items are often sorted prior to sale or consumption on the basis of their softness. Products such as blueberries, olives, cranberries, cherries, grape tomatoes, cherry tomatoes require such sorting. There are several mechanical systems used with varying degrees of success. These systems generally use the principle of soft fruit not rolling as freely as firm fruit. This is fairly effective when removing very soft material however it is not very sensitive for a food item that is only slightly soft. This product is often sorted by hand which is labour intensive and can lead to further damage. Very firm fruit such as cranberries are mechanically sorted with a berry bounce system, which is effective however it is often too slow for large-scale packers. Most small fruit grading and packing lines are capable of packing over 5000 lb per hour, which is well beyond the capacity of the cranberry bounce softness sorter.
The main reason for wanting to sort out the soft food items is to increase the product shelf life. The soft product tends to have a higher incidence of rots and decay. Softness can also be a function of maturity and over maturity can also contribute to reduce shelf life. Such food items are also commonly subject to pricing regimes that are product-quality dependent, so to match product quality to market expectations usually results in maximising returns to the product owner.
To address the quality matching issue, a product sorter is described. Any symmetrical item within a size range similar to a berry can be sorted on the basis of its softness using this method and apparatus. Other items may also be suitable, provided the fall involved in its characterisation is insufficient to create tissue damage causing subsequent susceptibility to premature quality degradation. The preferred embodiment of the invention utilises a shallow angle rebound (ricochet) so as to minimise the deformation energy imparted to the item during rebound, thereby minimising risk of tissue damage, while yet being sufficient to extract its ricochet energy signature.
This invention is superficially similar in principle to U.S. Pat. No. 6,541,725 (Acoustical apparatus and method for sorting objects) in which the procedure of rebounding an item off a surface is optimised for hard items such as nuts, which emit an acoustic deformation energy signature after leaving the impact surface. That technique requires a rigid and immovable rebound surface, and the introduction of a time delay after the impact to ensure the deformation energy signature is sampled at the appropriate time after rebound. Additionally, the deformation energy is released by acoustic radiation in air, therefore appropriately detected by microphone. In contrast, this invention extracts the deformation energy signature by conducted energy transfer while the food item impacts a resiliently mounted rebound surface and remains in contact with that surface. In this aspect its detection method is similar to a cherry sorter impact sensor (Younce & Davis, 1995, ASAE) but necessarily and fully integrates trajectory control into its functioning.